Development of the treatment system for water polluted with organic chlorine compounds by using photocatalysis in the gas-phase

Pollution of groundwater and soils with organic chlorine compounds，such as trichloroethylene and tetrachloroethylene has been serious problems，A system for the treatment of such compounds using a combination of aeration and gas-phase photocatalysis was developed in the present study.Experiments for the fundamental study to elucidate reaction mechanisms，etc.and the practical study for the development of the actual system were carried out.1。Results of the fundamental study by using a batch reactor are as follows；1)The photocatalytic degradation of trichloroethylene(Or Tetrachloroethylene)was accelerated，when a TiO ei D22西耶D2 photocatalyst was pre-illuminated with UV light before the reaction。This was supposed to be due to desorption of water molecules and hydroxyl groups from the surface of the TiO I D 22齐埃D2 photocatalysts.2)The second and third reactions were still accelerated，when the photocatalytic degradation reaction was repeated by using the same photocatalyst.3)Phosgene and dichloroacetylchloride were detected as the(Intermediate)products.The acceleration of the repeated reactions stated above was supposed to be due to the chain reaction initiated with such compounds.4)The fundamental study on reaction mechanisms was thought to give useful information to minimize formation of harmful by-products in the continuous reactor of a pilot-plant scale.2。Results of the practical study using a system of a pilot-plant are as follows；1)A pilot plant to treat organic chlorine compounds in the actual groundwater was constructed in success using the combination of aeration and photocatalysis.The groundwater polluted with tetrachloroethylene was well purified continuously.2)No harmful compounds over the standard were detected in the gaseous exhaust.3)The plant was operated continuously for five weeks。Practical data were obtained to show much possibility of the construction of actual larger plant。

Pollution of groundwater and soils with organic chlorine compounds, such as trichloroethylene and tetrachloroethylene has been serious problems, A system for the treatment of such compounds using a combination of aeration and gas-phase photocatalysis was developed in the present study. Experiments for the fundamental study to elucidate reaction mechanisms, etc. and the practical study for the development of the actual system were carried out.1. Results of the fundamental study by using a batch reactor are as follows ;1) The photocatalytic degradation of trichloroethylene (or tetrachloroethylene) was accelerated, when a TiOィイD22ィエD2 photocatalyst was pre-illuminated with UV light before the reaction. This was supposed to be due to desorption of water molecules and hydroxyl groups from the surface of the TiOィイD22ィエD2 photocatalysts.2) The second and third reactions were still accelerated, when the photocatalytic degradation reaction was repeated by using the same photocatalyst.3) Phosgene and dichloroacetylchloride were detected as the (intermediate) products. The acceleration of the repeated reactions stated above was supposed to be due to the chain reaction initiated with such compounds.4) The fundamental study on reaction mechanisms was thought to give useful information to minimize formation of harmful by-products in the continuous reactor of a pilot-plant scale.2. Results of the practical study using a system of a pilot-plant are as follows ;1) A pilot plant to treat organic chlorine compounds in the actual groundwater was constructed in success using the combination of aeration and photocatalysis. The groundwater polluted with tetrachloroethylene was well purified continuously.2) No harmful compounds over the standard were detected in the gaseous exhaust.3)The plant was operated continuously for five weeks. Practical data were obtained to show much possibility of the construction of actual larger plant.